Optimization of Protection Condition on the Stability of Castor (Ricinus communis) Oil Based Biodiesel using Response Surface Methodology

Abstract

The effects of designed protection conditions such as different antioxidants (propyl gallate, PG and Pyrogallol, PY), antioxidant concentration (30 – 600 ppm), temperature (30˚C -120˚C) and storage period (3 – 5 days) on the oxidation stability of castor biodiesel were investigated work was to assess the effect of the antioxidants on the oxidative stability of castor biodiesel. Using the American Standard for Testing Materials (ASTM) recommended protocols to determine the changes in the physicochemical properties (acid value, p-anisidine value, peroxide value, totox value, density, kinematic viscosity and refractive index) of the castor biodiesel were measured. The protection conditions were optimized using the Response Surface Methodology (RSM) according to the Box–Behnken Design (Design Expert version 11 Statistical Software). The analysis of variance (ANOVA) of propyl gallate showed concentration levels and temperature as the most important factors in the biodiesel oxidation, whereas the day of storage was one of the lowest factors with the p-value of < 0.05 for most indicated process variables of both linear and quadratic model terms were significant. The changes in some important physicochemical values are indication of degradation occurring in the biodiesel under the set storage condition. The optimal storage conditions were observed in propygallol with the acid value (0.985 mg KOH/g), p-anisidine value (7.650 mg KOH/g) and Totox value 4.005 (mEq/kg) with the overall desirability of 0.923 based on comparatively lower acid, p-anisidine and Totox values, followed by PG. The combined use of PY/PG antioxidants didn't show a synergic or additive result that makes the mixture of those antioxidants unsuitable to boost the biodiesel stability based on their relatively higher Totox Value.